The present invention relates to an improved apparatus for forming directional characteristics at the receiving end of a reflected beam ranging system utilizing acoustical or electromagnetic wave energy and for correlating the received signals, the apparatus employing a plurality of transducers arrranged in rotational symmetry in the transmitting-receiving plane, which transducers emit pulsating wave energy as the transmitted signal and which are connected for reception via a transmitting-receiving switch and possibly amplifiers with a scanner which repeatedly interrogates in succession the signals received by the transducers during one reflected-beam ranging period, with each switch position of the scanner being associated with one directional angle and each interrogation cycle for all transducers being associated with one revolution of the directional angle.
In order to determine the position of an object, a reflected-beam ranging system emits wave energy which is reflected by the object and received again by the ranging system. The time between transmission and reception of the signal corresponds to the distance between the reflecting object and the reflected-beam ranging system. In order to determine the direction of impingement of the reflected wave energy, signals for directional characteristics are formed in the reflected-beam ranging system from the signals received by the transducers, which directional characteristics lie in the transmitting-receiving plane in the shape of a fan, for example. The strongest signal produces the directional characteristic which points in the direction of the object.
German Offenlegungsschrift (Laid-Open Patent Application) No. 2,136,780, corresponding to U.S. Pat. No. 3,810,082 issued May 7th, 1974, to E. Arens, (the subject matter which is incorporated herein by reference) discloses a system in which the signals received by the transducers, which are disposed for example on a cylindrical base, are successively interrogated and then fed to a delaying chain. From the delaying chain the delayed received signals from a group of tranducers are read out according to given delay times to form a directional characteristic, are evaluated as to their amplitudes and are combined in an adder circuit. The delay periods and amplitude evaluations for the received signals depend on the position of the transducers of a group on the cylindrical base with reference to the direction of the directional characteristic to be formed. Since every signal group which is used to form a directional characteristic is disposed on the periphery of the cylindrical base offset by one transducer and the arrangement of the transducers within the group is always the same, the same delay periods result for each group and thus the same taps of the delaying chain and the same amplitude evaluations of the received signals. At the output of the adder circuit there appear, in synchronism with the interrogation of the transducers, a succession of signals for the adjacent directional characteristics.
In order to free the signals from interference, it is known to correlate the interferred with signals with the same but interference-free signals by means of a replica correlator. In the above-mentioned arrangement this would mean that the same number of replica correlators would have to be used as there are transducers on the cylindrical base. The reference function for the correlation could be, for example, the transmitted signal. However, due to the high technical expenditures involved for memories, multiplication and integration circuits, such an arrangement is impractical.